PART II – Optimal cell size, which many take for granted, is not as simple a thing as one might expect. The belief that cell size alone is responsible for bee size is not quite accurate. Rather, both cell size and inheritance determine ultimate bee size.Clearly, reported differences in cell size and in bee size between domestic (European) bees reared in large cells and Africanized honey bees reared in naturally built comb have often been misinterpreted. AHB cells are not Smaller, but domestic strains build cells that are Larger.

How Big

While AHB may produce slightly smaller cells (6), cell size is a poor diagnostic character due to the overlapping size ranges of AHB and natural comb or comb drawn from small commercial foundations (see “How Big” at right).

Could it be that the reproductive advantage reported for AHB over domestic bees occurs, at least in part, because AHB have not been subjected to artificial selection pressure for large body size and, as a result, build comb of a smaller size? This is a logical hypothesis if we assume that smaller bees and reduced cell size combine to increase the number of individual bees reared per unit area of comb and shorten the developmental time of the larval and papal stages. Moreover, accelerated spring buildup in smaller cells could lead to early drone production and, hence, a mating advantage of AHB. The logical extension of these hypotheses would suggest that domestic bees would be more competitive with Africanized bees if they were reared in hives with comb of natural cell size and had comparable developmental periods.

Realization of the importance of cell size might also provide a management tool against the Varroa mite. Recently, Message and Goncalves reported that, in Brazil, cell sizes for Africanized and domestic (European) honey bees averaged 4.5 to 4.8 and 5.0 to 51 mm per cell, respectively. They further reported that Varroa infestation rates were 4.8 and 11.5 percent, respectively. Camazine, (3) calculated female Varroa replacement rates for Africanized and domestic honey bees at 1.2 and 1.8 with drones present and 0.8 and 1.5 without drones, respectively. (A female Varroa replacement rate of less than 1.0 indicates that the mite population is declining while a 1.0 rate is indicative of zero population growth). Thus, we think that it may be possible to suppress Varroa populations in domestic colonies by using small strains of bees with shorter development times reared in smaller cells.

Cell size may impact a range of issues from the efficacy of queen excluders, given the variable size of bees that may be produced, to the susceptibility of colonies to disease, parasites and pesticides. Whether or not we can manage Africanized bees and Varroa mites using a combination of smaller brood cells and smaller bees remains to be seen. But, as Cheshire first suggested many years ago, it is possible that departures from the normal size of honey bees may cause or contribute to the severity of problems facing the beekeeping industry. We speculate that this line of reasoning might apply to problems such as tracheal mites (e.g. smaller tracheal openings in smaller bees might confer resistance to tracheal mites), winter mortality and other stress related losses (5). These issues deserve further study.

Some research is now in progress but much remains to be done. For those beekeepers interested in experimenting with cell size on their own, we have, in our early studies, found that packaged bees obtained from a single producer will readily draw out foundation of either 857 or 800 cells per dm2 (see Cell Size below). We simply placed one fully drawn comb in each hive with nine frames of foundation with the same cell size. We assumed that, during the period when the packaged bees were disassociated from comb, the workers would lose their memory of previous cell size and thus ensure that the bees would quickly adapt to the new size.

Cell sizes produced by packaged bees on two sizes of foundation.

Foundation Size

Cell Size

5.12

5.14 ± .09

5.36

5.36 ± .06

Based on 40 colonies per treatment, and 5 measurements per colony.

These data clearly demonstrate the ease with which a beekeeper can effectively reduce comb cell width in colonies. A corresponding reduction in bee size should follow without selection and breeding. However, simple methods are available for further reducing bee size through selective breeding (see our paper entitled “Managing Colony Genetics by Grafting and Selecting for Queens With Shorter Development Times” in the The American Bee Journal, November, 1989, pg. 717). Further reduction of cell width appears to follow in such a selection program. We now have samples of comb resulting from the annual insertion of new foundation (5.18 mm per cell) into colonies undergoing continued selection pressure for smaller bee size over a three-year period. Cell width in the most recently drawn comb measures 5.08 mm per cell. However, be cautioned that the extent to which such a program can or should be carried out is yet unclear.

The authors wish to thank H. Don who measured all foundation and mill specimens and C. Shipman who helped us assure the accuracy of our mathematics. We also thank all those people who kindly provided us with foundation and mills for examination.

1 Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty by the USDA and does not imply its approval to the exclusion of other products or vendors that may also be suitable.Ý U.S. Department of Agriculture, Agricultural Research Service, Carl Hayden Bee Research Center, 2000 E. Allen Road, Tucson, AZ 85719.